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Home >> Infiniti >> 2005 >> QX56 AWD >> Repair and Diagnosis >> Engine Performance >> Engine Control System >> DTC P0420, P0430: Three Way Catalyst Function >> Diagnostic Procedure
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Diagnostic Procedure

  1. CHECK EXHAUST SYSTEM 

    Visually check exhaust tubes and muffler for dent.

    OK or NG 

    1. OK: GO TO 2.
    2. NG: Repair or replace.
  2. CHECK EXHAUST GAS LEAK 
    1. Start engine and run it at idle.
    2. Listen for an exhaust gas leak before the three way catalyst (manifold).
      Fig 1: Checking Exhaust Gas Leak
      G02388856Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG 

    1. OK: GO TO 3.
    2. NG: Repair or replace.
  3. CHECK INTAKE AIR LEAK 

    Listen for an intake air leak after the mass air flow sensor.

    OK or NG 

    1. OK: GO TO 4.
    2. NG: Repair or replace.
  4. CHECK IGNITION TIMING 

    Check the following items. Refer to "BASIC INSPECTION ".

    CHECK IGNITION TIMING

    Items Specifications
    Target idle speed 650 +/- 50 RPM (in P or N position)
    Ignition timing 15 +/- 5° BTDC (in P or N position)

    OK or NG 

    1. OK: GO TO 5.
    2. NG: Follow the "BASIC INSPECTION ".
  5. CHECK INJECTORS 
    1. Stop engine and then turn ignition switch ON.
    2. Check voltage between ECM terminals 21, 22, 23, 40, 41, 42, 44, 63 and ground with CONSULT-II or tester.

      Refer to WIRING DIAGRAM  for Injectors, "WIRING DIAGRAM "

      1. Battery voltage should exist. 

    OK or NG 

    1. OK: GO TO 6.
    2. NG: Perform "DIAGNOSTIC PROCEDURE ".
    Fig 2: Checking Voltage Between ECM Terminals 21, 22, 23, 40, 41, 42, 44, 63 & Ground
    G02388857Courtesy of NISSAN MOTOR CO., U.S.A.
  6. CHECK FUNCTION OF IGNITION COIL-I 
    CAUTION: Do the following procedure in the place where ventilation is good without the combustible.
    1. Turn ignition switch OFF.
    2. Remove fuel pump fuse in IPDM E/R to release fuel pressure.
      NOTE: Do not use CONSULT-II to release fuel pressure, or fuel pressure applies again during the following procedure.
    3. Start engine.
    4. After engine stalls, crank it two or three times to release all fuel pressure.
    5. Turn ignition switch OFF.
    6. Remove all ignition coil harness connectors to avoid the electrical discharge from the ignition coils.
      Fig 3: Removing Fuel Pump Fuse In IPDM E/R To Release Fuel Pressure
      G02388858Courtesy of NISSAN MOTOR CO., U.S.A.
    7. Remove ignition coil and spark plug of the cylinder to be checked.
    8. Crank engine for 5 seconds or more to remove combustion gas in the cylinder.
    9. Connect spark plug and harness connector to ignition coil.
    10. Fix ignition coil using a rope etc. with gap of 13 - 17 mm between the edge of the spark plug and grounded metal portion as shown in the figure.
    11. Crank engine for about 3 seconds, and check whether spark is generated between the spark plug and the grounded metal portion.
      1. Spark should be generated. 
      CAUTION:
      • Do not approach to the spark plug and the ignition coil within 50cm. Be careful not to get an electrical shock while checking, because the electrical discharge voltage becomes 20kV or more.
      • It might cause to damage the ignition coil if the gap of more than 17 mm is taken.
      NOTE: When the gap is less than 13 mm, the spark might be generated even if the coil is malfunctioning.
      Fig 4: Checking Ignition Spark
      G02388859Courtesy of NISSAN MOTOR CO., U.S.A.

    OK or NG 

    1. OK: GO TO  10.
    2. NG: GO TO 7.
  7. CHECK FUNCTION OF IGNITION COIL-II 
    1. Turn ignition switch OFF.
    2. Disconnect spark plug and connect a known-good spark plug.
    3. Crank engine for about 3 seconds, and recheck whether spark is generated between the spark plug and the grounded metal portion.
      1. Spark should be generated. 

    OK or NG 

    1. OK: GO TO 8.
    2. NG: Check ignition coil, power transistor and their circuits. Refer to "IGNITION SIGNAL ".
  8. CHECK SPARK PLUG 

    Check the initial spark plug for fouling, etc.

    OK or NG 

    1. OK: Replace spark plug(s) with standard type one(s). For spark plug type, Refer to "CHANGING SPARK PLUGS "
    2. NG:
      1. Repair or clean spark plug.
      2. GO TO 9.
    Fig 5: Checking Spark Plug For Fouling
    G02388860Courtesy of NISSAN MOTOR CO., U.S.A.
  9. CHECK FUNCTION OF IGNITION COIL-III 
    1. Reconnect the initial spark plugs.
    2. Crank engine for about three seconds, and recheck whether spark is generated between the spark plug and the grounded portion.
      1. Spark should be generated. 

    OK or NG 

    1. OK: INSPECTION END 
    2. NG: Replace spark plug(s) with standard type one(s). For spark plug type, Refer to "CHANGING SPARK PLUGS ".
  10. CHECK INJECTOR 
    1. Turn ignition switch OFF.
    2. Remove injector assembly.

      Refer to "FUEL INJECTOR AND FUEL TUBE ".

      Keep fuel hose and all injectors connected to injector gallery.

    3. Disconnect all ignition coil harness connectors.
    4. Reconnect all injector harness connectors disconnected.
    5. Turn ignition switch ON.

      Make sure fuel does not drip from injector.

    OK or NG 

    1. OK (Does not drip.): GO TO 11.
    2. NG (Drips.): Replace the injector(s) from which fuel is dripping.
  11. CHECK INTERMITTENT INCIDENT 

    Refer to "TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT ".

    1. Trouble is fixed: INSPECTION END 
    2. Trouble is not fixed: Replace three way catalyst assembly.
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